Backwashing Filters with 4″ Top Holes

Fleck 2850 Filter, 21″ X 62″. Will support a service flow of up to 50 gallons per minute.

Most residential backwashing filters have 2.5″ threaded top holes in the mineral tank. Conventional “small” filter valves like the Fleck 5600, Fleck 2510, and Fleck 5810 screw into 2.5″ top holes. These control valves can be used on tanks up to 13″ in diameter. Beginning with 14″ tanks, most have 4″ top holes and require the use of larger filter valves, like the Fleck 2750, 2850, or 3150. Tanks with 4″ holes are available up to 24″ X 72″ in size. (The next larger size of tanks have a 6″ flange connection on top rather than a threaded hole.)

For want of better name, we call the filters made with the second size top hole 4″ filters. The filter above is from this group.

In general terms, filters of this size are for use in situations needing flow rates above 10 gallons per minute. Here is a chart that gives some typical uses with maximum effective service flow rates, in gallons per minute (GPM).

Tank Size in Inches

(Media Load with Most Media, in cubic feet)

Carbon Filter removing chlorine from city water

Katalox Light Filter removing iron from well water

Zeolite (Turbidex) filter removing sediment from well water.

14 X 65 (3.5)

10

11

21

16 X 65 (4)

14

14

25

18 X 65 (5)

18

18

28

21 X 62 (7)

24

24

32

24 X 72 (10)

30

32

62

30 X 72 (15)

50

49

73

36 X 72 (20)

70

70

125

Be aware that there can be great discrepancies among media when it comes to service flow rates and backwash requirements. For example,

Big Filter Prices

Prices of filters given below include control valve (mechanical timer), Structural Mineral Tank, Drain Line Flow Control, Riser with upper and lower baskets, media funnel, and gravel underbed. We pay shipping to lower-48 addresses. Usual lead time is about 4 days.

Tank Size in Inches

(Media Load with Most Media, in cubic feet)

Fleck 2750, 1″ Control

Part Number and price

Fleck 2850, 1.5″ Control

Part Number and Price

Fleck 3150, 2.0″ Control

Part Number and Price

14 X 65 (3.5)

BW102 – $986

BW281 – $1450

16 X 65 (4)

BW105 – $1055

BW282 – $1500

18 X 65 (5)

BW103 – $1299

BW283 – $1755

21 X 62 (7)

BW104 – $1464

BW284 – $1941

24 X 72 (10)

BW285 – $2415

BW290 – $2880

30 X 72 (15)

BW291 – $3760 (6″ Flange)

36 X 72 (20)

BW292 – $4225 (6″ Flange)

Prices above are for the filter only. Gravel underbed is included, but not filter media.

Filters may be ordered with or without media. If media is purchased with the filter, the filter will be set up to match the media. If no media is ordered, tell us your intended use for the filter and we will furnish it with an appropriate flow control device. There is no pre-shipment setup of control valves with the these filters, but we can suggest and help with setup after the purchase.